The invention relates to a trip device comprising setting selector switches designed to define first protection parameters representative of an overload or a short-circuit and accessible to a user, display means, a processing unit connected to current sensors and to the setting selector switches, the processing unit comprising:
first digital processing means connected to the current sensors and to the setting selector switches in order to perform basic protection functions, PA1 second digital processing means connected to the first processing means and to communication means enabling second protection parameters to be set by remote setting.
Known trip devices conventionally comprise potentiometers and/or selector switches on the front panel enabling the protection parameter settings to be adjusted. Others comprise a keypad combined with a display enabling the protection parameter settings to be adjusted and read. The latter trip devices also sometimes comprise means for remote setting of the parameters.
U.S. Pat. No. 5,311,392 describes a trip device comprising two microprocessor-based processing circuits. Such a trip device 1 is illustrated in FIG. 1. It comprises a first microprocessor-based processing circuit 2 designed to perform protection against overloads and short-circuits, i.e. the long delay, short delay, instantaneous and, if applicable, earth protection functions. This first processing circuit is conventionally connected to current sensors 3, to selector switches 4 located on a front panel of the trip device, to a cause of trip display device 5 and to a trip coil 6. It comprises a second microprocessor-based processing circuit 7 designed to perform communication functions and additional monitoring and protection functions (as regards voltage, phase displacement, power, frequency, etc). The second processing circuit 7 is connected to the first processing circuit by a two-way link. It is also connected to the current sensors 3 and to voltage sensors 8. It is also connected to a first interface 9 designed to be connected to a remote display device 10, and to a second interface 11 designed to be connected to a computer 12. The second processing circuit 7 also performs a backup protection function in case of malfunctioning of the first processing circuit. The unbroken line in FIG. 2 represents a time/current tripping curve used by the first processing circuit 2, taking into account the protection parameters defined by the selector switches 4.
The second processing circuit performs the backup function taking into account a second tripping curve represented in a broken line in FIG. 2. The protection parameters corresponding to the second tripping curve are systematically higher than the values set by the selector switches. They can be preset, unable to be modified by the user, or adjustable by means of the interfaces 9 and 11, or be set by a shift of the first curve. The second processing circuit is continuously supplied by an auxiliary power supply 13 and comprises a trip output connected to the trip coil 6. In normal operation, the first processing circuit 2 performs the current protection functions according to the current measured by the current sensors 3 and the parameters defined by the selector switches, the second processing circuit performing additional measuring and protection functions. In the event of a failure of the first processing circuit, the second processing circuit performs the current protection functions using the same current values measured by the current sensors 3 and the backup parameters corresponding to the second curve of FIG. 2.